ScienceDaily (Dec. 19, 2008) — The power of viruses is well documented in human history. Swarms of little viral Davids have repeatedly laid low the great Goliaths of human civilization, most famously in the devastating pandemics that swept the New World during European conquest and settlement.

In recent years, there has been growing evidence for the hypothesis that the effect of the pandemics in the Americas wasn't confined to killing indigenous peoples. Global climate appears to have been altered as well.

Stanford University researchers have conducted a comprehensive analysis of data detailing the amount of charcoal contained in soils and lake sediments at the sites of both pre-Columbian population centers in the Americas and in sparsely populated surrounding regions. They concluded that reforestation of agricultural lands—abandoned as the population collapsed—pulled so much carbon out of the atmosphere that it helped trigger a period of global cooling, at its most intense from approximately 1500 to 1750, known as the Little Ice Age.

"We estimate that the amount of carbon sequestered in the growing forests was about 10 to 50 percent of the total carbon that would have needed to come out of the atmosphere and oceans at that time to account for the observed changes in carbon dioxide concentrations," said Richard Nevle, visiting scholar in the Department of Geological and Environmental Sciences at Stanford. Nevle and Dennis Bird, professor in geological and environmental sciences, presented their study at the annual meeting of the American Geophysical Union on Dec. 17, 2008.

Nevle and Bird synthesized published data from charcoal records from 15 sediment cores extracted from lakes, soil samples from 17 population centers and 18 sites from the surrounding areas in Central and South America. They examined samples dating back 5,000 years.

What they found was a record of slowly increasing charcoal deposits, indicating increasing burning of forestland to convert it to cropland, as agricultural practices spread among the human population—until around 500 years ago: At that point, there was a precipitous drop in the amount of charcoal in the samples, coinciding with the precipitous drop in the human population in the Americas.

To verify their results, they checked their fire histories based on the charcoal data against records of carbon dioxide concentrations and carbon isotope ratios that were available.

"We looked at ice cores and tropical sponge records, which give us reliable proxies for the carbon isotope composition of atmospheric carbon dioxide. And it jumped out at us right away," Nevle said. "We saw a conspicuous increase in the isotope ratio of heavy carbon to light carbon. That gave us a sense that maybe we were looking at the right thing, because that is exactly what you would expect from reforestation."

During photosynthesis, plants prefer carbon dioxide containing the lighter isotope of carbon. Thus a massive reforestation event would not only decrease the amount of carbon dioxide in the atmosphere, but would also leave carbon dioxide in the atmosphere that was enriched in the heavy carbon isotope.

Other theories have been proposed to account for the cooling at the time of the Little Ice Age, as well as the anomalies in the concentration and carbon isotope ratios of atmospheric carbon dioxide associated with that period.

Variations in the amount of sunlight striking the Earth, caused by a drop in sunspot activity, could also be a factor in cooling down the globe, as could a flurry of volcanic activity in the late 16th century.

But the timing of these events doesn't fit with the observed onset of the carbon dioxide drop. These events don't begin until at least a century after carbon dioxide in the atmosphere began to decline and the ratio of heavy to light carbon isotopes in atmospheric carbon dioxide begins to increase.

Nevle and Bird don't attribute all of the cooling during the Little Ice Age to reforestation in the Americas.

"There are other causes at play," Nevle said. "But reforestation is certainly a first-order contributor."

flourbug

12-23-2008, 08:10 AM

so, its not just coincidence that after gasoline prices rose to record levels this summer and people drastically cut back their driving, it is now freeeezing cold?

Kassy

12-23-2008, 08:14 AM

The article above refers to reforestation after most of the population of the Americas died. I've read similar articles focusing on reforestation in Europe/England after the black death which some time before that.

See here:
http://www.boingboing.net/2006/02/27/black-death-triggere.html

Monitoring the ups and downs in abundance of cereal pollen (like buckwheat) and tree pollen (like birch and oak) enabled them to estimate changes in land-use between AD 1000 and 1500.

The team found an increase in cereal pollen from 1200 onwards (reflecting agricultural expansion), followed by a sudden dive around 1347, linked to the agricultural crisis caused by the arrival of the Black Death, most probably a bacterial disease spread by rat fleas...

"Between AD 1200 to 1300, we see a decrease in stomata and a sharp rise in atmospheric carbon dioxide, due to deforestation we think," says Dr van Hoof, whose findings are published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology.

But after AD 1350, the team found the pattern reversed, suggesting that atmospheric carbon dioxide fell, perhaps due to reforestation following the plague.

Also see this thread for a role of early humans in maybe warding of an ice ages by influencing the world through change in land use (rice farming and deforestation): http://curevents.org/showthread.php?t=6847

Kassy

12-23-2008, 08:15 AM

The article above refers to reforestation after most of the population of the Americas died. I've read similar articles focusing on reforestation in Europe/England after the black death which some time before that.

See here:
http://www.boingboing.net/2006/02/27/black-death-triggere.html

Monitoring the ups and downs in abundance of cereal pollen (like buckwheat) and tree pollen (like birch and oak) enabled them to estimate changes in land-use between AD 1000 and 1500.

The team found an increase in cereal pollen from 1200 onwards (reflecting agricultural expansion), followed by a sudden dive around 1347, linked to the agricultural crisis caused by the arrival of the Black Death, most probably a bacterial disease spread by rat fleas...

"Between AD 1200 to 1300, we see a decrease in stomata and a sharp rise in atmospheric carbon dioxide, due to deforestation we think," says Dr van Hoof, whose findings are published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology.

But after AD 1350, the team found the pattern reversed, suggesting that atmospheric carbon dioxide fell, perhaps due to reforestation following the plague.

Also see this thread for a role of early humans in maybe warding of an ice ages by influencing the world through change in land use (rice farming and deforestation): http://curevents.org/showthread.php?t=6847

so, its not just coincidence that after gasoline prices rose to record levels this summer and people drastically cut back their driving, it is now freeeezing cold?

The relation is not that direct but it'll help in the long run. For fun i checked if Canada's last white christmas coincided with the seventies oilcrisis but it was prior to that.

You can't see the climate reacting on such a short timescale anyway (all examples run over a timescale of decades to centuries) and now prices are somewhat down again people will go back to their usual driving habits so it'll be a small dent.

I do expect our current economic misery having much more real effect on climate change then all the cap & trade stuff. A lot less stuff is being hauled across the oceans and driven around the country and a lot less people are driving around to check out the same stuff...and it seems to have some staying power.

One of my favorite comments during the summer was a woman remarking on how high fuel prices where reshaping her shopping methods. She'd made a list of stuff to buy and started organizing her trips to minimize driving. :D

The main problem with fuel prices and our reactions to them is that they are merely a part of the problem.

In all historical examples humans had a profound effect on carbon sinks.
- warding of ice ages by removing the forest
or
- allowing for reforestation by dying en masse in Europe or the America's.

As you know we still have the corn ethanol and palm oil chicanery going on as ever and huge parts of the Amazon are chopped down for agriculture & livestock.

The examples above should hint at the urgency of addressing those problems along with the fuel consumption.

We need hard targets for areas where nature needs to be preserved and we need hard targets to reintroduce natural growth mainly in tropical areas. But that's much easier said then done because this also ties in with food and economic security for poorer nations and their people.

flourbug

12-23-2008, 09:06 AM

We need hard targets for areas where nature needs to be preserved and we need hard targets to reintroduce natural growth mainly in tropical areas. But that's much easier said then done because this also ties in with food and economic security for poorer nations and their people.

Which is one of the reasons why I'm supporting Florida's purchase of US Sugar lands in the Everglades. Many of my co-residents are against spending so much money during an economic disaster, but purchasing the land costs the same as the taxpayer funded bonuses those bailed out bank CEO's got as Christmas gifts. Our economy is screwed because our priorities are wrong. We can't afford to rescue privately owned businesses. We can't afford NOT to rescue the Everglades.

Fattail

12-23-2008, 11:10 AM

Kassy:

As you know we still have the corn ethanol and palm oil chicanery going on as ever and huge parts of the Amazon are chopped down for agriculture & livestock.

So what you are saying is, that without ethanol and palm oil it might actually be colder outside.